Episode #95 Still Keeping Patients Warm and Safe with Convective Warming Systems

Hello and welcome back to the Anesthesia Patient Safety Podcast.  My name is Alli Bechtel, and I am your host. Thank you for joining us for another show. Last week, we discussed two cases of thermal injuries sustained by patients following use of convective warming systems during surgery with general anesthesia. The authors Janik and Lewandowski proposed questions for the manufacturer of the warming system, Smiths Medical. Well, this week, we are back with the rapid response from Smiths Medical.

Before we dive into the episode today, we’d like to recognize ICU Medical, a major corporate supporter of APSF. ICU Medical has generously provided unrestricted support to further our vision that “no one shall be harmed by anesthesia care”. Thank you, ICU Medical – we wouldn’t be able to do all that we do without you!”

Our featured article today is “Convective Warming Systems – Maintaining Normothermia in the Operating Room” by Jesus Cabrera. Cabrera is the Senior Director of Medical Affairs for Smiths Medical. This article is in response to our featured article from last week, “Thermal Injury After Use of a Convective Warming System.” To follow along with us, head over to APSF.org and click on the Newsletter heading. First one down is the Current Issue. Then, scroll down and look in the left-hand column and click on the Rapid Response to questions from readers heading and then click on our featured article. I will include a link in the show notes as well.

Let’s take a look at the response now. Cabrera starts off by discussing the priority for quality and patient safety at Smiths Medical. This article will serve to review the potential causes for the thermal injuries that we discussed last week. The good news is that the patients injuries improved with conservative treatment. Now is the time to figure out what happened to help keep patients safe going forward. Smiths Medical has a standard procedure to follow for investigations related to product complaints and patient safety concerns. The first step is for the two Level 1 Equator Convective Warming Devices used in the cases that we discussed last week to be returned to Smiths Medical for testing. Both devices were found to be working appropriately including the alarm systems.

The next step in the standard procedure was for Smiths Medical to review their Periodic Safety Update Report. This report contains post-market data for the past five years related to the safety and performance of the marketed products. This device has been used quite a lot around the world over the past 10 years with over 40 million blankets sold in the past 5 years. The report did not point out any patterns of patient safety issues with the device and the device was found to be safe and acceptable for continued manufacture, sale, and distribution. The good news is that this report is available for repeated reviews going forward as well.

Now, let’s move on to the response by Smiths Medical about what may have occurred during these cases. This is based on the report and the discussion between the sales representative and the clinical team.

Cabrera starts off by highlighting the important point that thermal injuries are rare when the manufacturer’s instructions are followed. If we return to the Equator’s Operating Manual under Important Safety Information there is a warning statement that reads, “The hose nozzle must be connected to a Snuggle Warm convective warming blanket” and it continues, “Do not treat patients with the hose alone. Thermal injury may occur.” Check out Figure 1 in the article for a visual diagram about safely connecting the hose nozzle to the convective warming blanket. You can also find this in the Operator’s Manual under “Operating Instructions” and it is Step 4. For more information about safely using this device, Smiths Medical has a guide called, “Equator Convective Warming System Step-by-Step Guide.” In this guide, you can also find an illustration of the correct way to connect the hose nozzle into the collar ring of the blanket.

Next, Cabrera returns to the discussion of the hose nozzle or air manifold component of the device. If you remember from last week, the air manifold was missing during one case and the hose was directly connected to the blanket. The function of the air manifold is to connect the hose to the blanket and distribute air evenly. This is a critical piece of the device and safe operation may not be possible if this device is missing.

Now, let’s turn our attention to the impact of the type of surgery for these cases. Remember, both patients were undergoing robotic prostatectomy and it is time to dive into the literature since there have been concerns associated with this type of surgery reported in the literature. The studies include the following: “Anesthesia considerations for robotic-assisted laparoscopic prostatectomy: a review of 1,500 cases” by Danic and colleagues and “Anesthetic concerns for robotic-assisted laparoscopic radical prostatectomy” by Gainsburg. These reviews describe the positioning of the patients during the surgery in lithotomy and steep Trendelenburg, pneumoperitoneum, limited access to the patient, and the length of surgery leading to risks for nerve injuries as well as hemodynamic, respiratory, and cardiovascular effects. Temperature monitoring is important during these surgeries and convective warmers are often needed to maintain normothermia. It may be that during robotic prostatectomies there is a risk for thermal injuries since it may be difficult to secure the hose nozzle during this procedure in particular. In addition, when the arms are tucked and the warming blanket is tucked under the mattress at the patients sides, there is the potential for air flow restriction and this risk is increased if the nozzle is not connected appropriately to the patient. This could be a set up for a jet of hot air to be directed continuously over the patient’s skin for a length of time leading to a thermal injury. This situation is described in the Warnings of the Operator’s Manual.

One of the important outcomes from the meeting between the sales representatives and the clinical team at NorthShore University Health System is the discovery that several hose nozzles were missing from the convective warming devices. Replacements were delivered to the institution.

Cabrera wraps up the article by highlighting the long history of safe and effective use of the Level 1 Equator Convective Warming Systems all over the world. These cases provide an opportunity to review correct and safe use of these devices. Keep in mind that the hose nozzle otherwise known as the air manifold is a critical component required to connect the hose to the blanket for safe use. Do you use the Level 1 Equator Convective Warming System in your operating rooms? If so, when you are done listening to this podcast, go check out your devices and make sure that the hose nozzles are present and being used correctly according to the Operating Manual. You can bring Figure 1 from the article with you since this is a good visual representation of the set up and connection. Patient positioning during surgery is another consideration when using a convective warming device to ensure that the nozzle is connected correctly and there is no airflow restriction. Finally, last week we discussed the question of which temperature setting to use for patients under general anesthesia. According to the user’s manual, the highest temperature setting should only be used when needed to correct hypothermia quickly depending on the clinical situation and the highest temperature setting should only be used when necessary and the temperature decreased as soon as possible.

Thank you so much to Cabrera and Smiths Medical for your thoughtful response. This is an excellent review for the safe use of a common device in the operating room.

This is definitely a hot topic and we have one more article from the February 2022 APSF Newsletter Rapid Response section to discuss today. It is Convection Warmers and Burn Injury – Still a Clear and Present Danger” by Jeffrey Feldman. You can find this article in the same rapid response section as our first article. Feldman kicks off the article by highlighting the safety profile of convection warmers that have been used to prevent hypothermia in the operating room for millions of patients around the world each year. Convection warmers transfer heat to the skin which is then absorbed by the blood and distributed to the rest of the body leading to increased body temperature. Thermal injuries may occur when the heat is applied to the skin at a high enough temperature that it is greater than the capacity of the blood to absorb it leading to a burn injury. Convection warmers are capable of delivering high enough heat to cause thermal injuries and this is why the device must be used properly. It is important to make sure that the outlet hose is not used without the nozzle or a warming blanket to disperse the heat. The process of just using the convection warmer with the hose directed at the patient’s skin is called “hosing” and should not be used due to the known risk for thermal injury.

During the cases that we talked about last week, a warming blanket was used and the patients still sustained thermal injuries. However, there were potential causes for these injuries including the missing nozzle hose and the patients’ positioning with the warming blanket tucked in under the mattress. These cases provided an opportunity to engage with the manufacturer, Smiths Medical and review the operator’s manual for this device. Feldman writes, “It is clear, however, that for convection warmers to be effective, they must produce a certain amount of heat that can cause an injury if the device is not used properly.”

There is a call to action for anesthesia professionals using convection warmers to be knowledgeable about the correct and safe use of these devices. The positioning of the warming blanket and the use of the convection warmer must all take into consideration the type of surgery and patient’s positioning during the surgery. When the patient’s arms are tucked, the arms of the warming blanket may need to be tucked around the patient and under the mattress. This practice may lead to airflow restriction, so the question remains about how to safely use the warming blanket for patients whose arms are tucked during the surgery to prevent concentrating hot air delivery at the inlet site.

Feldman provides us with a summary of action items that anesthesia professionals can use right now to help keep patients safe from burns when using convection warmers especially because we need to continue to use these convection warmers with their established safety profile to prevent hypothermia in the operating room along with the warming blankets. It may be tempting to use the highest temperature setting automatically, but since our patients often have decreased sensation, are nonsensate, or have poor perfusion, we need to consider the existing safety warnings and weigh the risks and benefits. Normothermia may be achieved and maintained with the medium temperature setting or with only a short duration of using the highest temperature setting.   Going forward, we can continue to keep our patients safe and warm with the following recommendations.

1. “Never use the hose without a warming blanket properly connected. (We know that!)
2. Reserve the highest temperature setting for patients who are significantly hypothermic and require rapid correction.
3. Use the highest temperature setting for the shortest duration required to reach a clinically acceptable temperature.
4. The temperature setting selected for convection warmers should be guided by simultaneous measurement of body temperature with an internal temperature probe, especially when the highest output setting is used.”

Feldman reminds us that the goal is normothermia, but at this time, there is no data regarding the rate of temperature correction and anesthesia professionals must continue to use clinical judgement. It may be that patient’s with mild hypothermia and a temperature between 35-36 degree Celsius only require the medium temperature setting. For patients with body temperatures less than 35 degrees Celsius, the highest temperature setting may be used for a limited duration of time and then when the patient’s temperature is greater than 35 degrees, the temperature setting may be decreased to the medium setting. Clinicians will also need to keep in mind the room temperature as well as the patient’s body surface area when developing a plan to maintain normothermia in the operating room. An important part of the anesthesia plan is appropriate temperature monitoring and maintaining normothermia and this may involve a discussion with the surgery and nursing teams in the operating room about how to work together to keep patients safe and warm.

If you have any questions or comments from today’s show, please email us at [email protected]. Please keep in mind that the information in this show is provided for informational purposes only and does not constitute medical or legal advice. We hope that you will visit APSF.org for detailed information and check out the show notes for links to all the topics we discussed today.  If you have not done so already, we hope that you will rate us and leave a review on iTunes or wherever you get your podcasts and feel free to share this podcast with your friends and colleagues and anyone that you know who is interested in anesthesia patient safety. Plus, you can let us know that you are listening by tagging us @APSForg using the hashtag #APSFpodcast.

Until next time, stay vigilant so that no one shall be harmed by anesthesia care.

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